1. Field of the Invention
The present invention relates to a technology of polishing a capillary used for microinjection.
2. Description of the Related Art
Microinjection technique is used to inject a drug solution into a cell. The cell is penetrated by a tip of a capillary that is made of a hollow glass needle and filled with the drug solution. Generally, the tip of the capillary is processed to have a very small outer diameter of about 1 micrometer.
Even then, the capillary does not have enough penetrating ability with respect to cells such as floating cells, resulting in insufficient injection of the drug solution. To enhance the penetrating ability of the capillary, the tip can be subjected to angled-polishing or processed to have an even smaller diameter.
One method of angled-polishing is to subject the tip to focused ion beam (FIB) milling. Another method is to use a capillary polishing apparatus that includes a diamond polishing plate or an alumina polishing plate. For a more complete description of such a capillary polishing apparatus, reference may be had to, e.g., a website as follows:    Shoshin EM Corporation, “Sutter Instrument”, [online], [accessed on Jan. 11, 2007], Internet <URL: http://www.shoshinem.com/bv-10.htm>
However, in the case of FIB milling, the required setup is expensive, which increases the manufacturing cost of the capillary. In the case of using a conventional capillary polishing apparatus, a capillary having a tip diameter of about 1 micrometer is polished on a polishing plate having a surface roughness Ra of about 0.05 micrometer, which results in cracks around the tip. Moreover, if the tip diameter is further reduced, it is not possible to secure a discharge nozzle of sufficient size. As a result, the capillary gets clogged with the drug solution.